Quaternised UV-absorbers with tosylate anion are of significance for their substantivity to skin and hair as well as their mildness compared to the corresponding quaternary halides [Soap, Perfumery & Cosmetics, 29–34, March 1997].
U.S. Pat. No. 4,680,144 (1987) and U.S. Pat. No. 5,427,773 (1995) disclose preparations of these kind of cationic substantive photofilters like dodecyl dimethyl amino benzamido propyl dimethyl ammonium tosylate. In this process, a primary amino group of N,N-dimethyl propyl diamine is reacted with dimethyl amino benzoic acid to form an amidoamine and then the tertiary amino group of the amidoamine is quaternised with alkyl tosylate. Similarly, U.S. Pat. No. 6,613,340 (2003) discloses cationic tosylate salts from cinnamidoalkylamines following the same methodology. The procedures described in these patents are very tedious where alkyl tosylates that are used for quaternisation are in turn prepared from fatty alcohols and tosyl chloride. This tosylation reaction is done in a suitable solvent using stoichiometric quantities of tertiary amine bases like triethylamine or pyridine. The organic bases mop up the hydrochloric acid generated and the subsequent hydrochloride-base salt that is formed as a by-product has to be removed by washing the reaction mixture with water. This significantly increases the effluent load. Another disadvantage of this process from prior art is that the reaction for preparation of alkyl tosylates is carried out in either halogenated solvents like dichloromethane or aromatic solvents. Purification of alkyl tosylate also results in significant loss of yield and simultaneous increase in effluent treatment. This purification step is necessary due to the presence of unconverted fatty alcohols in alkyl tosylates. The quaternisation of cinnamidoalkylamines and/or benzamidoalkylamines with alkyl tosylate does not give quantitative conversion and hence after the purification step isolated yields of quaternised UV-absorbers range between 65 to 70% only.
In summary, all these factors make the process for making quaternised UV-absorbing tosylates not only tedious and expensive but also non-environment friendly. Hence, there is a need for a simple, quantitative and eco-friendly process for making these substantive UV-absorbers that are superior to the corresponding halides due to tosylate as counter ion.